Funding is requested to support the next meeting of the National Neurofibromatosis Foundation International Consortium for the Molecular Biology of NF1 and NF2 to be held June 20-22, 1999 at the Whitehead Institute in Cambridge, Massachusetts. Beginning in 1985, the NNFF Consortium meetings have served as the catalysts for many of the fundamental discoveries in the study of these important diseases of the nervous system. These meetings provide a regular forum to bring together basic researchers, geneticists, clinicians, and others familiar with NF1 and NF2 to share their latest research findings and experiences. NNFF Consortia have been instrumental in the rapid advances in the molecular understanding of NF1 and NF2, including the cloning of the responsible genes, establishment of diagnostic tests, exploration of gene function, development of animal models, and creation of infrastructure to establish a patient-clinician network to facilitate clinical trials. Following a recently established pattern, the 1999 Consortium meeting has been organized with a small format, which will be attended by invited speakers, session chairs and a small number of selected discussants. There will be five formal sessions, including an opening night keynote session. The four regular sessions will have 5 to 6 speakers each, including several junior investigators, and a session chair, who will provide an overview to the session and foster discussion. The speakers will be instructed to limit their presentations to approximately half of the allotted time, with the remainder dedicated to open discussion among all participants. The theme of the 1999 Consortium meeting is "NF1 and NF2: Defining Function," and the focus will be to explore the cell and molecular biological functions of these two genes through the use of biochemical, cell biological and in vivo approaches. This small format meeting, especially with the emphasis on open and active discussion, will maximize the chance for meaningful and potentially groundbreaking analysis of our current understanding of these issues. This meeting will also help to identify critical gaps in our knowledge and outline ideas, strategies and collaborations to address them. An improved understanding of the molecular basis of NF1 and NF2 has implication for disease pathogenesis, cancer biology generally, as well as a wide range of fundamental problems of cellular differentiation and development in the nervous system and beyond.